An asynchronous transfer mode (ATM) network provides an application program with a QoS connection-oriented service that has guaranteed bandwidths for sending Internet Protocol (IP) packets or “traffic.” To send the packets, the application requests a virtual circuit (VC) with an initial bandwidth. After the VC has been allocated to the application, an adaptation layer of the network determines how long to keep the VC open with the initial bandwidth assignment. As long as the sending rate of the packets matches the allocated bandwidth, then the VC is kept open, see H. Saran, S. Keshav, “An empirical Evaluation of Virtual Circuit Holding Times in IP over ATM Networks,” Proc. of INFOCOM 1994, Y. Afek, M. Cohen, E. Haalman, Y. Mansour, “Dynamic Bandwidth Allocation Policies,” 0743-166X/96 IEEE, and S. K. Biswas, R. Izmailov, “Design of a fair Bandwidth allocation Policy for VBR Traffic in ATM Networks,” IEEE/ACM Trans. On Networking, V:8, N:2, April 2000. However, if the application sends packets at a higher or lower rate than the allocated bandwidth, then there is a need to adjust the bandwidth of the allocated VC.
Periodic adaptation processes adjust, i.e., “renegotiate,” the allocated bandwidth at fixed time intervals. On the other hand, adaptive processes renegotiate the bandwidth as necessary, as long as the renegotiations are not too frequent. Renegotiating the bandwidth can be done in two ways. The existing VC can be closed, and a new VC can be allocated, or the allocation of the current VC can be adjusted, Y. Afek, M. Cohen, E. Haalman, Y. Mansour, “Dynamic Bandwidth Allocation Policies,” 0743-166X/96 IEEE. The later case is preferred because adjusting the bandwidth of an existing VC takes less time than closing and opening the VC.
When the data rate of the traffic fluctuates rapidly it is said to be “bursty.” This makes it a problem for a QoS router or server to determine exactly when to renegotiate bandwidth, and what the adjusted bandwidth should be, particularly with real-time traffic, .e.g., a “live” streaming video, at a utilization level greater than 98%.
M. Grossglauser, S. Keshav, and D. Tse, “RCBR: A Simple and Efficient Service for Multiple Time Scale Traffic,” in Proc. ACM SIGCOMM'95, pp. 219–230, August 1995, described an off-line method for bandwidth renegotiation. Their method determines an optimal schedule for traffic based on a complete knowledge of the traffic's required data rate over time. They assign a constant cost per renegotiation and per allocated bandwidth unit. That off-line method achieves 99% bandwidth utilization defined as a ratio of the average rate of the original stream to the average of a piecewise constant service rate, with one renegotiation on average every seven seconds. Even though the utilization achieved in that method is very close to 100%, their method cannot be used for renegotiating real-time traffic where a future behavior of the traffic is not known a priori.
Therefore, there is a need for a method and a system for optimally renegotiating bandwidth for real-time network traffic.